U.S. Departments of Agriculture and Health and Human Services have declined some researchers' move to include sustainability information in the 2015 update to the dietary guidelines on Tuesday.

Sustainability advocates claimed it is critical that more research be done into what foods are the most and least damaging to the environment.

"Not only should you [eat sustainably] for dietary health reasons but for the health of the planet," Executive director of the Sustainability Institute Kathleen Merrigan from George Washington University said. "We may not have all the answers, but we certainly know we better be raising the questions."

Time shared that meat represents the ultimate in unsustainable food products. For instance, meat goods for buyers leave an enormous carbon footprint given the resources they require which include water, land, fertilizer, food, among others. As a matter of fact, Environmental Working Group revealed that producing a kilogram of beef results in the release of 27 kilograms of carbon dioxide into the atmosphere.

Kathleen and her co-researchers suggested in a separate report published in the journal Science that consumers might want to consider reducing their intake of some health food products such as almonds, for example, due to the enormous amount of water it take to produce. However, she clarified that "it's not say we shouldn't be eating almonds," adding, "these are complicated issues."

Additionally, some fish falls into the same bucket like almonds: scientists-distinguished foods which unquestionably belong in a healthy diet but raise concerns in regards to sustainability, particularly in the long term.

The report in Science noted that the supply of some fish captured unsustainably could be susceptible if everyone in the U.S. trailed the USDA guidelines which suggest Americans to increase their seafood consumption. Further study is being piloted in the Netherlands which aims to evaluate which species in particular should be avoided. Too, experts said more research are needed.

Dietary guidelines are one place to start for Americans interested in healthy lifestyle. Expected to be updated by December, the document provides details on everything about vegetarianism to health questions about alcohol consumption. However, things can get so very tricky for people who want to know what's sustainable in addition to being healthy.